Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of the common general knowledge in the field.
Antimicrobial metal nanoparticles such as silver or copper nanoparticles are broad-spectrum antimicrobial materials used for different purposes including water purification and other hygiene-related products. However, these metal nanoparticles are known to be toxic and cannot be used as such in compositions for human use. They also have an impact on the environment.
The silver or copper nanoparticles have a tendency to agglomerate under certain conditions of pH and temperature which results in lowering of its antimicrobial activity and imparting colouration making the product aesthetically unpleasant and difficult to be incorporated in many products especially when the base is white or light coloured.
WO14052973 A1 (Stelo Technologies), discloses a method of making silver nanoparticles using an ascorbic acid derivative or an alpha-hydroxy carboxylic acid derivative as a reducing agent. The silver nanoparticles may be coated onto micro particles, embedded in hydrogel particles or coated with polysaccharide. The silver nanoparticles may be used in a wound dressing, a bandage, a fungal treatment product, a deodorant, a floss product, a toothpick, a dietary supplement, dental X-ray, a mouthwash, a toothpaste, acne or wound treatment product, skin scrub, and skin defoliate agent. In this process which comprises mixing silver salt with the reducing agent and then coprecipitating the nanoparticles formed on microparticles, the colour of the composite particles will be dark and will be unsuitable for personal care products especially when they have a white base.
KR20090018456 (Korea University Industrial and Academic Collaboration Foundation), discloses the preparation of silver zinc oxide nanocomposite by simultaneous mixing of silver and zinc sources with reducing agents in ethanolic medium. Simultaneous mixing of zinc source and silver salt leads to undesired dark coloration and lowers the antimicrobial efficacy.
RU2311804 C1 (Megrabjan), discloses bactericidal composition containing highly dispersed metallic silver stabilized with a protective material. The material was prepared by mixing silver salt, calcium salt and a base, which would lead to undesired dark coloration and lower antimicrobial efficacy.
JP11236304 (Dowa Electronics Materials Corp.), discloses a method of preparing silver particles embedded in calcium carbonate by a process of mixing silver salt and calcium carbonate and then calcining the material. The material obtained would have the problem of dark coloration and lower antimicrobial efficacy.
US2008/0156232 A1 (Crudden et.al, 2008) discloses a process for preparing antimicrobial additive particles in which the antimicrobial agent is dry blended with a cake-forming material and thereafter this dry blend is added to water. After this step, the aqueous slurry is allowed to harden.
WO2012/161603 A1 (Uniwersytet Jagiellonski) discloses yet another method. Hybrid material containing calcium carbonate microparticles with a polyelectrolyte additive and silver nanoparticles embedded in its structure are made by ultrasound-assisted co-precipitation. Trisodium citrate is added to aqueous solution of Silver nitrate followed by sonication at elevated temperature. To this a solution of Sodium carbonate containing a polyelectrolyte and calcium nitrate is added which subsequently leads to nano-Silver particles embedded in a matrix.
WO2011/075855 Al (Perlen Converting AG) discloses a method in which the composite material is made by flame-spray pyrolysis.
WO2003/076341 A1 (Apyron Technologies INC) also discloses particulate matter containing a carrier and an antimicrobial agent.
WO2006/015317 A1 (Acrymed INC), discloses a process for making silver compounds by mixing stoichiometric amounts of solutions of a silver salt such as silver nitrate or acetate with a corresponding alkali or alkaline earth metal salt of an organic anionic compound. When preparing silver compounds dispersed on carrier supports, the mixing step is carried out in the presence of insoluble carrier materials.
WO2012/158702 A1 (BASF) discloses a process of preparing antimicrobial metal composite by vaporizing an antimicrobial metal or antimicrobial metal salt such as silver, copper or salts thereof using an plasma system and cooling the formed vapour in the presence a fluidized gas filler powder. Alternatively, the filler or a filler precursor is entrained with the antimicrobial metal or antimicrobial metal precursor and vaporized and then upon cooling the antimicrobial metal vapour and filler vapor condense to form the composite.
U.S.2006/0243675 A1 (Shiue-Lian Lin) discloses a process in which the components are added to pure water and mixed and then the mixture is maintained 3 to 5 hours to produce a homogeneous mixture readily for use in the next step. In this process, no reducing agent is used.
WO2008/027950 A1 (Allen Thomas) discloses a process in which metal particles like silver, copper, or gold together with a surfactant such as benzalkonium chloride, are taken in a liquid medium also having a source of iodine and a substrate carrier having the same type of metal as the particles deposited onto. This leads to embedded microparticles
CN101999409 (Henan Huier) discloses a process in which 15 to 70 mass % of deionized water or tap water is placed for 16 to 36 hours at room temperature into a reactor. Solution of a nano carrier with zinc is added to the reactor which is then dispersed and emulsified under high-speed mixing and shearing for 6 to 20 minutes, while maintaining the temperature of liquid at 5 to 25 degree Celcius. Then a solution of a silver salt is added into the reactor and continuously dispersed and emulsified for 40 to 90 minutes. This is followed by spraying a solution of a reducing agent into the reactor at rate of 1.5 to 9.5 kg/minute continuously dispersed and emulsified for 30 to 60 minutes to obtain the antimicrobial disinfectant.
CN101195719 B (Cao) discloses composite material containing a carrier and antibacterial metal.
It has now been possible to solve the problems of the prior art and to form a light-coloured, broad spectrum antimicrobial particulate composition with good antimicrobial properties comprising antimicrobial metal particles and porous inorganic material selected from water insoluble inorganic materials and also provide a process for preparing the same.
It is an object of the present invention to provide light coloured antimicrobial particulate composition that has good antimicrobial properties.
Another object is to provide a process for preparing antimicrobial particulate composition that has good antimicrobial properties.
It is yet another object of the present invention to provide an antimicrobial particulate composition that has good antimicrobial properties and aesthetically suitable for incorporation in personal care or hygiene compositions. It is especially beneficial for use where the base of the personal care or hygiene composition is white or light coloured.
In addition to killing bacteria, these materials are also capable of acting in killing virus.